The hows and whys are apparently unimportant. What matters is this: you, represented by a double-pointing pair of ASCII glyphs, are trapped in a devious labyrinth. Your goal, however, is not to escape, but rather to survive: in the maze with you are a number of Beasts, looking like slim sinister Hs. If they find you, they will eat away one of your lives.
Your weapons? None. However, nearly all of the walls in this maze can be pushed, like Sokoban crates... only indefinitely stackable. If you are able to line up wall segments and wait until a Beast enters into a gap between them, you should be able to close the gap on top of him, pushing the walls shut and making Beastly pulp. Maneuvre carefully, though, for once the wall segments are backed against the outside walls, you can only pull them back into "live", useful territory on certain levels. Also, you may hit a snag against solid-coloured immobile walls, preventing your stack from mashing the intended Beast. (Further complicating things, these immobile, "static" walls become deadly to the touch on later levels!)
On harder levels, you get to meet the whole Beast family, Super-Beasts, eggs and the Hatched Beasts that emerge from them. Meaner and tougher, they possess enhanced abilities, such as only being crushable against immobile walls or being able to turn the tables and push walls back at you (how quickly the crusher is become the crushee!)